Pulse shaper for inductive transmitters

ABSTRACT

A pulse shaper for inductive transmitters, in particular inductive crankshaft angle transmitters on internal combustion engines is suggested, wherein a Schmitt-trigger is connected with the output of the transmitter. A peak value detector (D1,C) is connected with the output of the transmitter and means are provided which set the trigger threshold of the Schmitt-trigger in dependency on the output of the peak value detector.

STATE OF THE ART

The invention is based on a pulse shaper for inductive transmitters, inparticular crankshaft angle transmitters on internal combustion enginesin accordance with the type of the main claim.

A pulse shaper for inductive transmitters is already known from thepublication "Motor-Elektronik", Robert Bosch GmbH, 1983. The inductivetransmitter is a crankshaft angle transmitter on an internal combustionengine which emits an alternate voltage. In order to process thisalternated voltage in an electronic control device for the internalcombustion engine, the alternate voltage is reshaped into rectangularcurrent pulses. A Schmitt-trigger is provided as a pulse shaper for sucha purpose. Thereby, the stable hysteresis of the Schmitt-triggersimultaneously increases the nonsensitivity with respect to lowinterferences. However, erroneous pulses are generated at the output ofthe Schmitt-trigger during interferences which extend beyond thehysteresis threshold of the Schmitt-trigger.

ADVANTAGES OF THE INVENTION

In contrast thereto, the pulse shaper in accordance with the inventionand in accordance with the type of the main claim is advantageous inthat at least one trigger threshold of the Schmitt trigger is notfixedly adjusted, but is adjusted by the peak value dectector independency on a peak value subsequent to the previously processedsignal. Thus, a pulse shaping is provided which is aadaptively dependenton different transmitter amplitudes thus providing an improved safetyagainst interference. If the subsequent processing of the shaped pulserequires a phase correct picking up of the transmitter signal, it isfurthermore advantageous to fixedly set a trigger threshold of theSchmitt-trigger, in particular to the zero passage of the transmittervoltage.

DRAWING

One exemplified embodiment of the invention is illustrated in thedrawings and is explained in detail in the subsequent description.Thereby, the single FIGURE illustates the electrical circuit diagram ofa pulse shaper in accordance with the invention.

DESCRIPTION OF THE EXEMPLIFIED EMBODIMENT

The FIGURE illustrates a circuit diagram of an inductive transmitterwith a subsequent series connected pulse shaper being operated by anoperating voltage U_(B) and a reference voltage U_(O). For this purpose,the inductivity L of an inductive transmitter, which for purposes ofsimplification is not illustrated, is connected in series with tworesistors R1, R2. Thus, the connecting point of the voltage divider R1,R2 represents the output of the transmitter. When a transmission voltageU_(G) is induced in inductivity L, the divider voltage at the output ofthe transmitter is changed accordingly.

Negative peak values of the output voltage of the transmitter are pickedup by a peak value detector consisting of a diode D1 and a capacity C.Furthermore, two resistors R4, R3 are connected in series between thecapacity C and the output of the transmitter. From the connecting pointof the resistors R4, R3 the detected negative peak values are fed to theinverting or minus input of a first differential amplifier V1. Theoutput of the transmitter is connected by means of a resistor R8 withthe non-inverting plus input of the second differential amplifier V2.

Each of the differential amplifiers V1, V2 is an operational amplifierhaving open-collector-output transistor. The outputs of the amplifiershave low resistance when the voltage on the minus input exceeds theinverting or voltage at the non-inverting or plus input and have a highresistance when the voltage on the plus input exceeds the voltage on theminus input.

The plus input of the first differential amplifier V1 is at a fixedpotential determined by a voltage divider R5, R6 and R7 which isconnected between the operating voltage U_(B) and the reference voltageU_(O). The connection point of a low Ohm resistor R7 and resistor R6 isconnected to the output of the first differential amplifier V1 through afeedback resistor R9. Since the resistor R7 has very low Ohms withrespect to the resistors R6, R5 the potential on the plus input of thedifferential amplifier V1 is only slightly changed by the feedbackthrough resistor 9 when the first differential amplifier V1 switches.Nevertheless, a positive feedback is obtained which controls switchingcharacteristics of the first differential amplifier.

The second differential amplifier V2 is connected with its minus inputto the output of the first differential amplifier V1. The output of thesecond differential amplifier is connected to the operating voltageU_(B) by means of a pull-up-resistor R11, and is directly connected withan output terminal at which the shaped pulses can be picked up asvoltage U_(A) The output of the second differential amplifier V2 isfuthermore connected through a resistor R10 to the cathode of a seconddiode D2, whose anode is connected with the plus input of the seconddifferential amplifier V2.

At a starting condition, i.e. when the induced transmitter voltage U_(G)-0 and no current flows through the capacity C, the potential of theminus input of the first differential amplifier V1 is equal to that atthe output of the transmitter, i.e., at the connected point of theresistors R1, R2. The resistors R5, R6 and R7 are dimensioned in such away that the same potential is applied at the connecting point of theresistors R6 and R7 and a somewhat higher potential at the plus input ofV1. Hence, at the starting condition the output of V1 has a highresistance and the same potential is at the minus input of V2 as at thetransmitter output.

Assuming that the output of the amplifier V2 has a high resistance andhas been pulled by the pull up-resistor R11 to U_(B), diode D2 is inblocking condition. The potential at the plus input is set through theresistor R8 to the potential at the output of the transmitter.

When a negative voltage U_(G) is induced across the inductivity L thevoltage on the plus input of the second differential amplifier V2follows the voltage at the output of the transmitter through resistorR8. If this voltage falls below the potential at the minus input of thesecond differential amplifier V2 is switched on and a positive feedbackis performed on the plus input through resistor R10 and the diode D2, sothat the second differential amplifier V2 does not switch back during arenewed zero crossing of the transmitter signal. Simultaneously thecapacity C is charged to the negative peak value of the transmittervoltage U_(G) through diode D 1 and the resistor R2. The voltage on theminus input of the first differential amplifier V1 depends on thenegative stored voltage on capacity C, from the momentary voltage at thetransmitter output and the dividing ratio of the resistors R3, R4.

During a positive induced voltage U_(G) across the inductivity L theratio of the resistors R3, R4 as well as the voltage on the capacity Calso determine at what time point the potential of the minus input ofthe first differential amplifier V1 exceeds the potential on the plusinput. Then the output of the first differential amplifier V1 isswitched on and a voltage is applied to the minus input of the seconddifferential amplifier V2 which is lower than that on the plus input byabout the forward voltage of diode D2. Now, the second differentialamplifier V2 switches over to high resistance and its ouput resumesthrough the resistor R11 the value operating voltage U_(B). Thus, thediode D2 is again in blocking condition.

During the next induced negative transmission voltage U_(G) across theinductivity L, the second differential amplifier V2 will switch on againwhen the voltage on the plus input of the second differential amplifierV2 falls below the voltage of the minus input and thereby below thevoltage drop across resistor R7. Therefore, the total arrangementconstitutes a Schmitt-trigger which operates with a fixed triggerthreshold, whose voltage level is set by the voltage drop on theresistor R7, and whose other trigger threshold is a switch voltage whichis dependent on the previous negative peak value of the transmittervoltage.

We claim:
 1. A pulse shaper for inductive transmitters, in particularinductive crankshaft angle transmitters on internal combustion engines,comprising a Schmitt trigger which includes a first and a seconddifferential amplifier each having two inputs; first setting meansconnected to one input of the first amplifier to apply thereto asubstantially fixed potential during an equilibrium condition of theSchmitt trigger; a peak value detector for coupling via said firstsetting means an inductive transmitter to the one input of the firstamplifier, said detector including a detecting diode and a capacity forstoring a detected peak value signal; second setting means connected tothe other input of the first amplifier to set a fixed trigger threshold;the output of the first amplifier being connected to one input of thesecond amplifier and the other input of the second amplifier beingconnected to said inductive transmitter; a feedback diode connectedbetween the output and the other input of the second amplifier, thefeedback diode being in blocking condition when the second amplifier isswitched off; and feedback means connected between the output of thefirst amplifier and the second setting means to adjust another triggerthreshold whose value depends on a previously detected peak value signalstored in said capacity.
 2. A pulse shaper as defined in claim 1 whereinsaid inductive transmitter is connected in series with a voltage dividerwhose connection point represents the output of the transmitter.
 3. Apulse shaper as defined in claim 2 wherein said detecting diode and saidcapacity are connected in series between said output of the transmitterand a reference voltage line, and said first setting means including avoltage divider bridging said detecting diode and being series connectedwith said capacity.
 4. A pulse shaper as defined in claim 1 wherein saiddifferential amplifiers are operational amplifiers wherein said oneinputs are inverting inputs and the other inputs are non-invertinginputs.